Tetherless and Batteryless Soft Navigators and Grippers

Remotely controllable soft actuators have promising potential applications in many fields including soft robotics, exploration, and invasion medical treatment. Shape memory polymers could store and release energy, resulting in shape deformation, and have been regarded as promising candidates to fabricate untethered soft robots. Herein, an untethered and battery-free soft navigator and gripper based on a shape memory hydrogel is presented. The shape memory hydrogel is obtained through hydrogen bonding between gelatin and tannic acid, and the hydrogel displays excellent shape memory properties on the basis of hydrogen bonding and the coil-triple helix transition of gelatin. Moreover, Fe3O4 nanoparticles are introduced to endow the hydrogel magnetic responsiveness and photothermal conversion capacity. Finally, the shape memory hydrogel in a stretched state is assembled with an inert hydrogel to achieve a bilayer hydrogel actuator, which could produce complex shape transformation due to the shape recovery of the shape memory layer induced by heat or light. Taking advantage of the magnetically control and light-responsive shape deformation, remotely controllable soft grippers that could navigate through tortuous paths and grasp objects from a hard-to-reach place have been accomplished. This approach will inspire the design and fabrication of novel shape memory hydrogels as remotely controllable soft robots.

Highly Stretchable, Self-Adhesive, Antidrying Ionic Conductive Organohydrogels for Strain Sensors

As flexible wearable devices, hydrogel sensors have attracted extensive attention in the field of soft electronics. However, the application or long-term stability of conventional hydrogels at extreme temperatures remains a challenge due to the presence of water. Antifreezing and antidrying ionic conductive organohydrogels were prepared using cellulose nanocrystals and gelatin as raw materials, and the hydrogels were prepared in a water/glycerol binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 584.35%) and firmness (up to 0.16 MPa). As the binary solvent easily forms strong hydrogen bonds with water molecules, experiments show that the organohydrogels exhibit excellent freezing and drying (7 days). The organohydrogels maintain conductivity and stable sensitivity at a temperature range (-50 °C-50 °C) and after long-term storage (7 days). Moreover, the organohydrogel-based wearable sensors with a gauge factor of 6.47 (strain, 0-400%) could detect human motions. Therefore, multifunctional organohydrogel wearable sensors with antifreezing and antidrying properties have promising potential for human body monitoring under a broad range of environmental conditions.

Nanocellulose-based sensors in medical/clinical applications: The state-of-the-art review

In recent years, the considerable importance of healthcare and the indispensable appeal of curative issues, particularly the diagnosis of diseases, have propelled the invention of sensing platforms. With the development of nanotechnology, the integration of nanomaterials in such platforms has been much focused on, boosting their functionality in many fields. In this direction, there has been rapid growth in the utilisation of nanocellulose in sensors with medical applications. Indeed, this natural nanomaterial benefits from striking features, such as biocompatibility, cytocompatibility and low toxicity, as well as unprecedented physical and chemical properties. In this review, different classifications of nanocellulose-based sensors (biosensors, chemical and physical sensors), alongside some subcategories manufactured for health monitoring, stand out. Moreover, the types of nanocellulose and their roles in such sensors are discussed.

Development of Gelatin-Based Shape-Memory Polymer Scaffolds with Fast Responsive Performance and Enhanced Mechanical Properties for Tissue Engineering Applications

Shape-memory polymers (SMPs) can be defined as a reversibly changing form through deformation and recovery by external stimuli. However, there remain application limitations of SMPs, such as complicated preparation processes and slow shape recovery. Here, we designed gelatin-based shape-memory scaffolds by a facile dipping method in tannic acid solution. The shape-memory effect of scaffolds was attributed to the hydrogen bond between gelatin and tannic acid, which acts as the net point. Moreover, gelatin (Gel)/oxidized gellan gum (OGG)/calcium chloride (Ca) was intended to induce faster and more stable shape-memory behavior through the introduction of a Schiff base reaction. The chemical, morphological, physicochemical, and mechanical properties of the fabricated scaffolds were evaluated, and those results showed that the Gel/OGG/Ca had improved mechanical properties and structural stability compared with other scaffold groups. Additionally, Gel/OGG/Ca exhibited excellent shape-recovery behavior of 95.8% at 37 °C. As a consequence, the proposed scaffolds can be fixed to the temporary shape at 25 °C in just 1 s and recovered to the original shape at 37 °C within 30 s, implying a great potential for minimally invasive implantation.

The model pH-controlled delivery system based on gelatin-tannin hydrogels containing ferrous ascorbate: iron releasein vitro

Hydrogels have become an essential class among all biomaterials. The specialized biomaterials are highly valued in the field of biomedical applications. One of the problems in wound management is local microelement deficiency associated with extensive wound lesions. The significant lack of elemental iron in the human body leads to serious consequences and prolongs treatment. The synthesis of gelatin-tannin hydrogels with ion delivery function is proposed in this study. The ability to release ions in low acid solution is a sphere of great interest. The pH drop in the wound cavity is usually associated with the contamination of some bacterial cultures. pH-controlled delivery of iron in buffer solutions (рН = 5.5/6.4/7.4) was considered for these hydrogels. The kinetics of iron release was determined by visible spectroscopy. Theoretical models were applied to describe the process of ion delivery. The structure of materials was examined by IR-spectroscopy and demonstrated the incorporation of ferrous ascorbate into hydrogel matrix. Thermal analysis was used to point out the key differences in thermal behavior by isoconversional methods (Flynn-Wall-Ozawa/Kissinger-Akahira-Sunose). The mechanical properties of the materials have been studied. The effect of iron ascorbate on polymer network parameters was discussed. The current study demonstrated the possibility of obtaining gelatin-tannin hydrogels for pH-dependent iron delivery. That provides future perspectives to expand the set of releasing microelements for biomedical applications.

Tannic acid: a versatile polyphenol for design of biomedical hydrogels

Tannic acid (TA), a natural polyphenol, is a hydrolysable amphiphilic tannin derivative of gallic acid with several galloyl groups in its structure. Tannic acid interacts with various organic, inorganic, hydrophilic, and hydrophobic materials such as proteins and polysaccharides via hydrogen bonding, electrostatic, coordinative bonding, and hydrophobic interactions. Tannic acid has been studied for various biomedical applications as a natural crosslinker with anti-inflammatory, antibacterial, and anticancer activities. In this review, we focus on TA-based hydrogels for biomaterials engineering to help biomaterials scientists and engineers better realize TA's potential in the design and fabrication of novel hydrogel biomaterials. The interactions of TA with various natural or synthetic compounds are deliberated, discussing parameters that affect TA-material interactions thus providing a fundamental set of criteria for utilizing TA in hydrogels for tissue healing and regeneration. The review also discusses the merits and demerits of using TA in developing hydrogels either through direct incorporation in the hydrogel formulation or indirectly via immersing the final product in a TA solution. In general, TA is a natural bioactive molecule with diverse potential for engineering biomedical hydrogels.